Key: Under fire MP Paul Foster-Bell 'working hard'

Prime Minister John Key is defending his under fire backbench MP Paul Foster-Bell, who's had 12 staff leave in just three years, and is one of the highest spending Wellington-based MPs.

Newshub on Sunday revealed allegations of unhappy staff, some of whom were forced to resign because of relationship breakdowns with Mr Foster-Bell. One former staffer told Newshub the list MP is a bully.

Newshub also revealed Mr Foster-Bell spent more than $60,000 on travel and accommodation last year, which was more than fellow Wellington-based National list MPs Chris Bishop and Brett Hudson combined.

Mr Key appeared on Paul Henry this morning, and was asked why Mr Foster-Bell had such high spending costs.

"He's busy, he's working hard," was the Prime Minister's reply.

When asked what he was busy doing, the Prime Minister conceded.

"I have no idea. I don't organise his diary. I'm not his PA, I'm his boss," he says.

Mr Foster-Bell isn't commenting, telling Newshub: "it would be inappropriate to discuss any employment matters. In terms of my travel, I believe all my travel was within the rules, and was for a Parliamentary purpose."